Twitter will likely become flooded with ads — much as Facebook has been — if it launches its own self-serve advertising mechanism this quarter, as reported by TechCrunch's Ingrid Lunden.

Twitter's "Ads API" — an application protocol interface that allows advertisers and ad agencies to plug and serve ads directly onto Twitter — is more than 18 months overdue. Reuters reported it was on its way in July 2011.

Facebook, of course, has its own Ads API, which is one reason it has more than 100,000 clients paying it $1.33 billion a quarter to run ads on the social network. Advertisers have launched promoted tweets and trends on Twitter, but until now those types of promotions have been fairly unobtrusive.

It's not clear what ads served through an API would look like, but there would likely be a lot of them. A source who intends to use the new API when it becomes available simply told us it would be "HUGE" — when it arrives.

The API has likely been what Nihal Mehta, who runs tweet-retargeting ad company LocalResponse, calls a "massive reverse engineering problem," because Twitter has so little targeting data on its users compared to Facebook. (Facebook users give Facebook lots of data about themselves that advertisers can target; the reverse is true on Twitter, where people don't even use their real names.)

The API comes shortly after investment firm BlackRock took an $80 million stake in Twitter. Coincidence? Or do Twitter's new bedfellows now want to see solid revenues backing their money?